Apparatus for selective electric signaling.



No. 714,83l. Patented Dec. 2,1902? J; S. STONE.

APPARATUS FOR SELECTIVE ELECTRIC- S|GNALlNG-. 1

(Application filed Jan. 23, 1901) (No Model.)

5 Sheets-Sheef In W W JEES E5:

M0. 7l4,83l. Patented Dec. 2. I902. J. S. STONE.

APPARATUS FOB SELECTIVE ELECTRIC SIGNALING. (Application med Jan. 28,1901.

(NqModeL) 5 Sheets-Sheet 2 Mo. 7l4,83l. Patented Dec. 2.11902.

J. S. STONE.

APPARATUS FOR SELECTIVE ELECTRIC SIGNALING.

(Application filed Jan. 28, 1901.)

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m. 7|4,as|. Patented mung-1.19112.

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APPARATUS FOR SELECTIVE ELECTRIC SIGNALING. (Application mod Jan. 28,1901.)

m @j m (No Model.) fishujs-rslhaai No. 7|4,83|. Patented Dec. 2, I902.

J. S. @TUNE.

APPARATUSIOR SELECTIVE ELECTRIC SIGNALING Application filed Jan flii.1901.)

(No Model.) 5 shaeisflihaet 5.

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a when the stations are not connected by a connatural or forced electricvibrations in a hori- JOHN STONE STONE, OF BOSTQN, MASSACHUSETTS,ASSIGNOR TO LOUIS E. WVHICHER, ALEXANDER P. BROWNE, AND BRAINERD T.,JUDKINS,

TRUSTEES.

APPARATUS Fo a SELECTIVE ELECTRIC SIGNALING.

SPECIFICATION forming part of Letters latent No. 714,831, dated December2, 1902.

Original application filed February 8, 1900. Serial No. 4,505- Dividedand this application filed Jaimary 23, 1901. Serial No. 44,384. (Nomodel.) v

To all whom it may concern:

Be it known that I, JOHN STONE-STONE, a citizen of the United States,residing at Boston, in the county of Suffolk and State of Mas- 5sachusetts, have invented certain new ,and

useful Improvements in Apparatus for Select ive Electric Signaling, ofwhich the following is a specification. 4

My invention relates to the art of trans other by means ofelectromagnetic waves without the use of wires to guide the waves totheir destination; and it relates more particularly to the system ofsuch transmission in which the electromagnetic waves are developed byproducing electric vibrations in an elevated conductor, preferablyvertically elevated.

Here'tofore in signaling between two stations by means ofelectromagnetic waves ducting-wire. certain disadvantageous'limitationshave been observed which greatly militated against thecommercial value of the methods employed. When the electromagnetic wavesare developed by producing zontal conduct0r,the attenuation of the wavesso developed as they travel away from the.

conductor is'found to be so great as to very seriously limit thedistance to which they may be transmitted and effectively received, thechief cause of this observed phenomenon probably being that owing to thehorizontal position of the conductor the plane of polarization of thewaves is such as to cause therapid absorption of theenergy of the wavesby .the conducting-surface ot' the earth or ;water over which theytravel. This difliculty has been overcome by a method of developing thewaves which consists in prod ucing natural electric wibrations in averticallyelevated conductor, in which case the plane of polarization ofthe wave so produced is at quadratu rewith that of the waves which maybedeveloped inahorizontalwire, and in case of the vertical conductortheattenuation of the waves is observed to be very much less mittingintelligence from one station .to an effectively received at muchgreater distances. A limitation of the commercial utility of this systemis,however,observed,which fore been found possible, so far as I amaware, to direct signals sent OlllifI'Olll atransmitterstation to theparticular receiving-station with which it is desired to'communicate tothe ex'- clusiou of other receiving-stations equipped with equally ormore sensitive receiving apparatus and located within the radius ofinfluence of the sendingrstation. Electromagnetic waves have also beendeveloped by producing natural or forced electric oscillations in loopsor coils of wire at the transmittingstation and also by means of thedischarge of electricity between two conducting spheres, cylinders, orcones; but in such cases the sphere of influence is so limited as togreatly restrict the commercial utility of these two methods ofdeveloping the signal waves. In fine, the method of signaling by meansof electromagnetic waves between stations not connected by aconducting-wire, in which method the electromagnetic waves are de-'veloped by electric vibrations in an elevated conductor, has greatadvantages over the other existing or proposed methods for accomplishingthis purpose in which the electromagnetic waves are developed byothermeans, since in thecase of the waves developed by the elevated-conductormethod the waves ma y be transmitted to and efiectively received atgreater distances than by the other systems, but whereas in the systemsemploying the other methods of generating the waves the signalsdeveloped may, at least theoretically, be directed to the particularreceiving-station with whichit is desired to communicate to tions in the.neighborhood. It has heretofore been found impossible, so far as Iknow, to accomplish this purpose in thesystememploying an elevatedconductor or wire as the source of the electromagnetic waves.

The object of thisinvention isto overcome the exclusion of other similarreceiving-stathan in the case of the horizontal conductor, so that thesewaves may be transmitted to and it depends upon the fact thatit has notheretothe hereinbefore-described limitation to the l mit their signalseach to a particular receiving-station simultaneously or otherwisewithout mutual interference.

It is'also the object of the invention to provide means whereby each ofa plurality of transmitting and receiving stations in such a system maybe enabled to selectively place itself in communication with any otherstation to the exclusion of all the remaining stations.

It is further the object of the present invention to enable the verticalor elevated condoctor in such a system to be made the source of simpleharmonic electromagnetic waves of any desired frequency independent ofits lengthandothergeometricalconstants. Thus the frequency impressedupon the elevated conductor may or may not be the same as the n'aturalperiod or fundamental of such conductor; but, as will be hereinafterexplained, an elevated conductor that is aperiodic may be employed andis best adapted for use when the apparatus is to be used successivelyfor different frequencies, and such aperiodic elevated conductor islikewise the preferred form of elevated conductor when two or morefrequencies are to be simultaneously impressed upon or received by asingle elevated conductor; but forced simple harmonic electricvibrations of different periodicities may each be separately impressedupon a difierent elevated conductor, and the several energies of theresulting electromagnetic waves may be selectively conveyed each to aseparate translating device.

Before proceeding to describe the invention certain fundamentalprinciples relative to electrical vibrations should be stated, as theseprinciples are involved in the art of signaling by means of what. may becalled unguided electromagnetic waves.

'Ifthe electrical equilibrium of a conductor be abruptly disturbed andthe conductor thereafter be left to itself, electric currents will flowin the conductor, which tend to ultimately restore the condition ofelectrical equilibrium. These currents may be either unidirectional oroscillatory in character, dependingupon the relation between theprincipal electromagnetic constants of the conductor-t'.. e.., upon itselectromagnetic and electrostatic capacities and its resistance. Thesephenomena are analogous to the mechanical phenomena which are observedwhen the mechanical equilibrium of a system is abruptly disturbed andthe system is thereafter left to itself. In the case of a mechanicalsystem motions re sult which tend to restore the mechanical equilibriumof the sys: tern. These motions may consist either of a .unidirectionaldisplacement or of to-and-fro vibrations of the system or parts of thesystem, depending upon the relations which sub sist between theprincipal mechanical constants of the system-i. e., its moments of massand elasticity and its friction coefficients. In general thedetermination of the relations which must subsist in order that anoscillatory restoration of equilibrium shall take place either in anelectric or in a mechanical system and the determination of the periodof these oscillations is very difficult; but in certain simple casesboth the determination of the conditions for an oscillatory restorationof equilibrium and of the period of these oscillations is quite'simple.

An example of a simple mechanical system capable of an oscillatoryrestoration of equilibrium is to be found in the torsional pendulum,which consists of a highly-elastic wire fixed at one end and supportingat its other extremity a heavy mass called the bob. If a torsionalstress be imparted to the wire of this pendulum by turning the bob aboutthe axis of the wire and the bob be then abruptly released, the pendulumwill in general execute isochronous oscillations about the axis of thesuspending-wire in the process of restoration of equilibrium.- Anexample of a simple electrical system capable of an oscillatoryrestoration of equilibrium is to be found in the case of a circuitconsisting simply of a condenser and a coil without iron in its core,

drawings, in which 0 is a condenser, and I is a coil without iron in itscore. If a charge of electricity be imparted to the condenser coil, asshown in Fig. 1, an isochronous oscillatory current will in general bedeveloped in the circuit in the process of restoration of its electricalequilibrium. Such a simple circuit asthat shown in Fig. 1 is known as asystem with a single degree of freedom,

when its equilibrium is abruptly disturbed and it is then left to itselfare known as the natural vibrations or oscillations of the system. Thesevibrations begin with a maximum of amplitude and gradually die away iaccordance withwhat is known as an exponential law and are what areknown as f. simple harmonic vibrations. They may be representedgraphically, as in Fig. 2, in which A is a curve drawn to rectangularcoordinates, in which the ordinates represent instantaneous values ofcurrent strength and the abscissae represent times. When two suchsimplecircuits are associated together inductively, as shown in Fig. 3, thesystem so formed is known as a system of two degrees of freedom, and inthe oscillatory restorations of equilibriumcurrents, as shown in Fig. 4.In general if n l simple circuits, as shown in Fig. 1, be assoand theelectric oscillations which it supports as shown in Figure l of theaccompanying and if its electrodes be then connected to the 2'. e., inthe natural vibrations in such cirharmonic in character, but in generalconsist what are termed forced vibrations, and in elated together inductive or by inductive connections a system of at least it degrees offreedom results, and

the natural oscillations of such a system will therefore consist of thesuperposition of at least n currents. It is, moreover, a fact that thedifferent simple harmonic components. of the oscillations which togetherconstitute the oscillatory restoration of equilibrium of acornplexsystem are in general not the same as those of the separate simplecircuits when these circuits are isolated from one another;

but the presence of each simple circuit modifies the natural period ofeach of the other circuits with which it isassociated. Thus in aparticular case if there be two simple circuits, the first with anatural period of .004

of a 'secoud when isolated and the second with a period of .0025 of asecond when isolated, these circuits when inductively connected, asshown in Fig. 3, may have an oscillatory restoration of equilibrium, ofwhich the simple harmonic. components are .00444 of a second and .00159of a second, showing that the inductive association of the ,circuitstogether has increased the natural period of the high-period circuit anddecreased the natural period of the low-period circuit. It

is, moreover, to be remembered that during the restoration of electricequilibrium cur-4 rents of each of the periods are found'in each of thecircuits of the connected system.-

Sofar we have considered the natural vibrations of electric systems-i.a, the electric vibrations by means of which the electric been abruptlydestroyed and the circuits are that'complex circuits-will in generalhave.

complex electric'oscillations. We have, moreover, seen that the naturalperiod of oscillations depended upon the electromagnetic constantsof thecircuit in the case of a simple circuit and thateach of the periods ofoscillation in the case of a complex or of interrelated circuitsdepended upon the electromagnetic constants, of each of the interrelatedcircuits but besides the ability to execute natural vibrations oroscillations both electric and mechanical systems are capable ofsupporting a system either by con- 7 equilibrium of circuits is restoredafter it has i the case of forced vibrations the period of the whether,it be a simple circuit or a complex the forced vibrations or of simplecircuits,

will also be simple harmonic and of the same period as that of theimpressed force. 7 In present systems of signaling by means conductor isemployed as the source of electromagnetic radiations the electricoscillations are of the kind hereinbefore described as naturalvibrations, the vertical conductor being charged to a high potentialrelative to the surrounding earth and permitted to ab tric' sparkbetween two ball-electrodes. In such a. method of developing theelectromagneticwaves the oscillations are necessarily of a complexcharacter, and therefore the resulting electromagnetic waves are of acomplex character and consist of a great variety of superimposed simpleharmonic vibrations of difierent frequencies. sist of a simple harmonicvibration of lower periodthan all the others, known as the fundamental,with a great variety of simple harmonies of higher periodicitysuperimposed thereon. the receiving-station is capable of receivingand'responding to vibrations of a great 'variety of frequencies, so thatthe electromagnetic waves which emanate from one vertical conductor usedas a transmitter are capable of exciting vibrations in any othervertical wire as a receiver, and for this reason anytransmitting-station in a system of this character will operate anyreceiving-station within its sphere of influence, and the messages fromthe transmitting-station will not be selectively received by theparticular receiving-station with which it is desired to communicate,but will interfere with the operation of other receiving-stations withinits sphere of influence, thereby preventing them from properlyresponding to the signals of the transmittingstat-ions from which theyare intended to receive their signals.

By my invention the vertical conductor of the transmitting-station ismade the source of electromagnetic waves of but a single periodicity,and the translating apparatus at the receiving-station is caused" to beselectively responsive to waves of but a single-periodicity, so that thetransmitting apparatus corresponds to a tuning-fork','sending but asingle simple musical tone, and the receiving apparatus corresponds toan acoustic resonator capable of absorbing the energy of that singlesimple musical t-one only. When, how-' ever, the elevated conductor isaperiodic, it is adapted to receive or transmit all frequencies, andaccordinglysa single aperiodic elevated conductor different frequencyafter the manner now well known in the art of multiple telegraphy bywire conductors.

When a single-elevated conductor is who made a source of a plurality ofsingle waves currents resulting from this impressed forts ofelectromagnetic waves in which a vertical 7 The vibrations con-Similarly the vertical conductor-at may be associated with a: pluralityof local-circuits. each attuned to a ruptly discharge to earth bymcansof an elecother frequency upon the conductor.

of difierent frequencies and when, moreovert these signal-waves are tobe simultaneously developed, it is obviously necessary that the trainsof waves of different frequencies developed in the elevated conductorshall be independent of each other-i. e., it is necessary that theelectric vibrations of one freless be hereinafter fully described inorder to add to the completeness of the specification. When theapparatus at a particular station is attuned 'to the same periodicity asthat of the electromagnetic waves emanating from a 0 I particulartransmitting-station, then this receiving-station will respond to and becapable of selectively receiving messages from that particulartransmitting-station to the exclusion of messages simultaneously orotherwise sent from other transmittingstations in the. neighborhoodwhich generate electromagnetic waves of dilferent periodicities.Moreover, by my invention the operator at the transmitting or receivingstation may at will adjust the apparatus at his command in such a way asto place himself in communication with any one of a number of stationsin the neighborhood by bringing his apparatus into resonance with theperiodicity employed by the station with which intercommunication isdesired.

' In order that the vertical conductor at the transmitting-station shallgenerate harmonic electromagnetic waves of but a single frequency, Icause the electric vibrations in the conductor to be of asimple harmoniccharacter, and this in turn I-accomplish by producing what aresubstantially forced electric vibrations in the vertical conductor inlieu of producing natural vibrations in the conductor, as has heretoforebeen practiced. In order that the electric translating apparatus at thereceiving station shall be operated having reference to the drawingswhich accompany and form a part of this specification.

The same letters, so far as may be, regresent similar parts in all thefigures.

Figures 1 to 4 are diagrams already referred to. Fig. 5 is a diagramillustrating one arrangement of the transmitting-station. Fig. 6 is adiagram illustrating an arrangement of the receiving-station.illustrating another form of the transmittingstation. Fig. 8 is adiagram illustrating another form of the receiving-station. Figs. 9 and15 are diagrams illustrating a detail of the construction at bothtransmitting and receiving stations. Figs. 10 and 11 are diagramsillustrative of the connection of the co-. herer at thereceiving-stations. Fig. 12 is a diagram illustrating the connection ofacoudenser-telephone at the receiving station. Figs. 13 and 16 arediagrams illustrative of forms of transmitter-stations capable ofdeveloping signal-waves of two different frequencies. Figs. 14 and 17are diagrams illustrative of forms of receiving-stations capable ofreceiving selectively signal-waves of two different frequencies.

In the drawings, V represents a vertical or virtually vertical conductorgrounded by the earth connection E. v

M, M, M,and M are ind action-coils whose Fig. 7 is a diagram primary-andsecondary wires are 1,, 1' 1" v generator at develops an alternatingelectromotive force of moderate frequency, which when the key It isdepressed develops a current in the primary circuit of the transformerM. v The transformer M is so designed as'to transform the electromotiveforce in the primary circuit to a very high electromotive force in thesecondary. As the potential difference at the terminals of the secondaryI rises the charge in the condenser 0 increases till the potentialdifference is s'uflicient to break down the dielectric at the spark-gap3. When this occurs, the condenser O discharges through the spark at s,the primary I ,-and the inductance-coil L. This discharge is oscillatoryin character and of very high frequency, as will be explainedhereinafter. The highfrequency current so developed passing through theprimary I induces a corresponding high frequency electromotive force andcurrent in the secondary I and forced elec-- tric vibrations result inthe vertical conductor V, which are practically of a simpleharmonic'character;

These simple harmonic vi'-.

,"bratio'ns'ih the conductor V develop electro- "si'mpl turn, onimpinging upon the vertical con-- magnttic waves, which are alsopractically harmonic in character, andthese, in

doctor at the receiving-station develop therein corresponding simpleharmonic vibrations i; oflike frequency.

In the organization illustrated in Fig. -6 the simple harmonicelectromagnetic waves of a given frequency or periodicity impinging uponthevertical conductor V develop thereincorrespouding electricalvibrations of like frequency.- By means of the induction-coil Mavibratory electrom otive force corresponding in frequency to theelectric'vibrations in t the conductor V is induced in the secondarycircuit I L C 0'.

If the frequency of this induced electromotive force is that to whichthe circuit I, LO 0' is attuned,-there will-be a maximum potentialdifference developed at theplates of the condenser O, and this potentialwill operate the coherer K. vWhen the coherer K operates, the resistanceof the circuit B R K is enormously diminished and the battery B developsacurrent which operates the translating device R. The decoherer (notshown in the drawings) is thereby set in operation, and as soon as theimpulse passes the coherer is restored to its sensitive condition. If,however, the frequency of the electromagnetic waves which impinge uponthe veltical conductor V of the receiving station depicted in Fig. 6 isnot the same as that'to which thecircuit I L C Ois attuned, theelectromotive force induced in this circuit will be dilferent fromthatto which the circuit will respond by virtue of resonance, and therewill be but a negligible potential difference developed at the plates ofthe condenser 0. Under these circumstance the coherer K will not beoperated and the-signals will not actuate the translating device B.

When transmitting-stations and a corvesponding number ofreceiving-stations are employed, by adjusting the electromagneticconstantsof the circuits atthe various stations these circuits maybe soproportioned or tuned that the energy of the electromagnetic wavesemanating from any given transmitting-station will be selectivelyreceived and absorbed at a given receiving-station.

Before proceeding to a description of the operation of the other twoforms of transmitting and receiving stations (shown'in Figs.

7 and 8) it is to be noted that the condenser charges of condensers isapproximately infrom which designed that the product of the capacity ofthe condenser by the inductance of the circuit is made numerically verysmall. Moreover, the oscillations in the circuit s I L are approximatelysimple harmonic in character and are practically unaffected by theinductive association with the vertical wire because of the auxiliaryinductance furnished by the coil L, it being capable of demonstrationthat if by means of the coil L the inductanceof the circuit L I sisrendered large compared to the mutual inductance between the circuit andthe vertical wire the natural oscillations which will take place in thecircuit s I L will be practically unatfect: ed by the inductiveassociation with the vertical wire and will therefore be practically ofa simple harmonic character, as in the case of the isolated simplecircuit shown in Fig. 1. The principlemay for the present purpose'bestated oscillators, each such as that shown in Fig.1, are inductivelyassociated with each other, as in Fig. 3, the system is a system of twodegrees of freedom, and the natural period of oscillation of each simplecircuit is modified by the presence of the other; but if the pro-.versely proportional to the square root of the ,go I thus: that whentwo simple 1 portions of the circuits be such that the prodnot of theinductance of the two circuits is large compared to the mutualinductance between the circuits the natural period of oscillation ofeach of the circuits becomes practically the same as if the circuitswere isolated. It, further, the electric equilibrium of the circuit .9 IL be abruptly disturbed and the circuit be then left without impressedforce-,the oscillations whichare developed in it induce correspondingoscillations in the vertical wire, which oscillations are virtuallyforced vibrations corresponding in frequency with the naturaloscillations developed in the circuits I L and beingpracticallyindlependcut as regards their frequency of the constants ofthe second circuit in which they are induced.

The mathematical expression for the frequencyto which a circuit isresonant when it is isolated from all. other circuits-4 e., ,has but asingle degree of freedom-is well known and may be stated as follows:

where n is the frequency, C is the capacity, L is the inductance, and pis the periodicity which equals 21m. In the case of a circuit of twodegrees offreedom, however, in order. to make the component circuitseach responsive to the. same frequency as when isolated-in other words,to overcome the modifying effect of the mutual inductance of eachcircuit upon the other-4t is necessary to consider in the case ofinductive relation the expression:

. M (L a M; 0,10 2 l) where C, L, are the capacity and inductance of thefirst circuit 0 L R are the capacity, inductance, and resistance,respectively, of the second circuit and M, is the mutual inductance ofthe circuits. From these expressions careful consideration will showthat the effective inductance of the first circuit has been modified byits inductive relation with the second circuit, and it is:

7 M2 IW L 121 11 1 1" 2 1 1p C1 Similarly we have to consider theexpression:

1 M2 I12 p(L1p 01 p) from which it will be seen that the effectiveinductance of the second circuit has been modified by its inductiverelation with the first circuit and is These two ind-uctances L, and Lare the apparent inductanoes which each of these circuits would have ifacting as a primary to induce simple harmonic vibrations of frequency11. in the other. It is therefore necessary in order to overcome themodifying eflect of the mutual inductance on either circuit to add tothat circuit an auxiliary inductance-coil of inductance large comparedto the term of the form a 1 b t) BM 1.)

' or at least so large that when it is added to I The vertical wire maywith advantage be so constructed asto be highly resonant to a particularfrequency, and the harmonic vibrations impressed thereon may withadvantage be of that frequency. The construction of such a vertical wireis shown and described in other applications of mine now pending. 7

At the receiving-station shown in Fig. 6 the inductance coil L isintroduced in .order to supply auxiliary inductance and to permit of thecircuit CO I, L-being' attuned to a partical conductor and thegenerating and translating devices, respectively.

Inthe transmitter arrangements illustrated in Fig. 7 the circuit C I LI, is attuned to the same-period as the circuit C L I s and merelytendsto wee'dout and thereby screen the vertical wire from any harmonicswhich may exist in the current developed in the circuit C L I, s. Thisscreening action of an interposed resonance-circuitis due to thewellk'nown property of such circuits by which a" resonant circuit favorsthe development in it of simple harmonic currents of the period to whichit is attuned and strongly opposes the development in it of simpleharmonic currents of other periodicities. In this organization anordinary spark-coil, (shown at M':,) equipped in the usualway with aninterrupterp and condenser C",is employed, the current being supplied bythe battery B. The operation of this organization is substantially thesame as that of the organization shown in Fig. 5, hereinbeforedescribed,except for the screening action of the circuit C I L I, andneed not,therefore,' be further described. Suffice it to say that whenthe source of vibratory currents is particularly rich in harmonics anysuitable number of resonant circuits each attuned to the desiredfrequency may be connected inductively in series, as shown in Figs. 9and 15, and interposed between the generating device and the verticalconductor for the purpose 'of screening the vertical conductor from theundesirable harmonics.

In the organization illustrated in 'Fig. 8 the electric resonator C I, L1,, interposed between the vertical conductor and the circuit containingthe coherer, is attuned to the same period as the circuit L O C" I, andacts to screen the coherer-circuit from the effect of all currentsdeveloped in the vertical conductor save that of thecurrent of theparticular period to which the receiving-station is IIO , i stationsofthe type shown in Fig. 7 associated intended to respond. 'Asin the caseof the" transmitting-station, any suitableuumher of resonantcircuits,,each attuned to the particular period to which the station isdesired fSuchci-rcuits so interposed serve to screen t therecei'ver fromthe effects of all currents to p y doctor that are not of the period towhich which may be induced in the verticalcom the receiving-station isintended to respond. No mention has heretofore been made of ,thefunction of the condensers shown at C inFig. 6 and at C" in Fig. 8, asthose con-v densers are not essentialto the tuning of the circuits inwhich they are placed, but merely serve to exclude the current of thebatteries B from the resonant circuits. In order that these'condensersmay not appreciably afiect the tuning of the circuits iri which they areincluded, and thereby lower the resonant rise of potential at the platesof the condensers C and (shown in Figs. 6 and 8,) they are soconstructed as to have large capacities compared to the capacities of Cand O in Figs. 6 and 8, respectively. p

In Figs. 6 and 8 the coherers K are shown connected in shunt-circuit tothe condensers in shunt-circuit to the coil L Q and C, respectively; butthey may be connected serially'in the resonant circuit, as

shown in Fig. 10,0r they maybe connected 7 and condenser O, as shown inFig. 11.

Though a coherer has been shown and described in the specification asthe means'of detecting the presence of oscillations in the receivingresonant circuits, under which circumstances it operates as atelegraphic relay to control a local-battery circuit including anelectric translating device, any other suitable electroreceptive devicemay be employed to receive the signal-as, for example, acondenser-telephone. When a condenser-telephone is employed as areceiver, the receiving resonant circuit may be that illustrated in Fig.12, in which 0 is the condenser-telephone and also thecapacity by whichthe circuit L GO I is attuned.

and 17 illustrates methodsof associating the apparatus hereinbeforedescribed, and illusalready described in connection with Figs. I

6, 7, 8, and 9. For the sake of clearness only trated inyFigs. 5-, 6, 7,8, and 9, when two or more stations are to be associated with a commonelevated conductor. The operation of each individual station is the sameas that two stations are shown associated with the common elevatedconductor V in the draw- An inspection of thed rawings will show thatFigs. 13 and '16 illustrate two transmitting- .with a common elevatedconductor, whereas The apparatus shown in Figs. 13, 1 4, 15, 16,-

letters of reference in the case ofone of the.

stations and not to the letters ofreference of the other station.

The operation of each of the transmittingstations in Figs. 13 and 16'isidentical with that of the transmitting-station illustrated in Fig. 7,and the operation of each .of the receiving-stations shown in Figs. 14and 17 is identical with the operation of the receivingstationillustrated in Fig. 8.

To illustrate, the step-up transformer or spark-coil M" in Figs. 13 and16 is equipped with an interrupter p and condenser C', and the currentis supplied by the battery B. When the key It: is depressed, a highpotential is developed in the secondary of M". As the potentialdifiereuce. at the terminals of the secondary of M" rises the condenserC is charged till the resulting potential diflerence at s is sufficientto break down the spark-gap 8. When this occurs, the condenser C"discharges through the spark at s, the primary of M, and theinductance-coil L". This cirwo: receiving-sta cuit is attuned to a givenhigh frequency, and f the oscillatory current which results is thereforeof that frequency. This current induces a similar current in theinterposed resonant circuit L M G M attuned to the same frequency, whichcurrent in turn induces 3. currentof corresponding frequency in thecon-* ductorV M E. I

Passing now to the operation of the receivbe-remarked that since theoperation of each of these. stations is identical with the operation ofthe receiving-station shown in Fig. 8 the energy of the waves of oneparticular frequency will be absorbed by one of the receiving-stationsand the energy of the waves of another particular frequency will beabsorbed by the other receiving-station. This selective reception of theenergy of waves of a particular frequency is independent of thenumber ofWaves of difierent frequencies which may be simultaneously present.

It is to be here noted that the above-described methods ofsimultaneouslytransmittingand receiving space-telegraph messages by acommon elevatedconductor are not de scribed as the preferred methods,but that any way of associating a plurality of the stations .shown inFigs. 5, 6, 7, and 8 with a vertical conductor will result in a systemfor simultaneously transmitting and receiving space-telegraph signals,owingto the fact that these staling-stations shown in Figs. 14 and 17,it may tions are in themselves inherently selective and dove opment ofvibrations of diiferent froquenciesin the'elevated conductor and ofselectively absorbing the energy of different frethe branch circuits M Min quencies, since .Figs. 16 and 17 are not in themselves selective andsince the elevated conductors in Figs. 13

- them in single inverse proportion to their electromagnetic impedancesand are not selective except for a slight reaction due to the associatedcircuits 0 M L and C M L,. These reactions, so far from tending to makethe branches selective to the frequencies to which their associatedcircuits are intended to respond, will, in fact, cause them to opposemore strongly currents of these frequencies than those to which theassociated circuits are not attuned. Again,itisobviousthattheinductanceof the coil M in Fig. 13 is merely an additional impedancein theelevated conductor, which, to say the least, cannot assist in thedevelopment of vibrations in the elevated conductor impressed by circuit0' M L M The same is obviously true of the coil M in the elevatedconductor with reference to the operation of the circuit C M L. Nowpassing to the transmitting-station shown at Fig.

' 16, it is obvious that the vibrations communicated by the circuit C ML to the elevated conductor V are subject to a shunt due to the coil Min the other branch of the elevated conductor, and, conversely, thevibrations developed in the elevated conductor by the as sociatedcircuit O M L are subject to a shunt due to the coil-M in the otherbranch of the elevated conductor. Finally, the coil M in the elevatedconductor in Fig. 14 can at best only present an impedance to the wavesintended to be received by the circuit O M L,, and, conversely, the coilM,in the elevated conductor can at best only present an impedance to thevibration s'intended to be received by the circuit C M L. 4

In constructing the various parts of the apparatus shown and describedin this specification there is great latitude as to the special formsthat may be given them; but it must be remembered that when a circuit isto be tuned and it is desired to gain a high degree of resonance bothelectrostatic and magnetic hysteresis must be carefully excluded fromthe resonant circuit. For this reason alliron should be excluded fromthe coils in the resonant circuits, and solid dielectrics shouldnotordinarily be employed in the condensers. These injunctions apply to theconstruction of resonant circuits attuned to vry high frere capable ofcausing the independent quencies, but not with the same force to theconstruction of resonant circuits .to be tuned to low frequencies.Another precaution to be taken in the construction of the apparatusincluded in the resonant circuits when very high-frequency currents areemployed is that conductors between which there exists-a considerablepotential difierence during the op eration of the apparatus shall bekept as" far apart as practical, because of the excessivedisplacement-currents which tend to flow in the case of high-frequencycurrents. For this reason it will often be found to be convenient tobuild the coils the form of flat spirals instead of long spirals ofseveral layers, as is the usual construction of coils. Flat spirals withthe turns well separated in orderto ininimize the displacemen t-currentsbetween the turns are, however, by no means the only forms of coilsadapted to be used in conjunction with air-condensers for the purpose oftuning circuits to high frequencies andmay often be neither. the bestnor most convenient form of coil to employ. Therefore in defining thecharacter of thecoils to be employed for this purpose it will be ofadvantage to first give the general theoretical considerations whichlead to a special construction of the coils and to then give a practicalguide to the manner of designing the coils for a particular f requencyorrange of frequencies.

A coil or solenoid as usually constructed consists of niany turns ofcotton or silk insulated wire wound on an .insulating-core,-such as aglass or ebonite tube or a wooden spool, the consecutive turns beingseparated only by the thin. insulating coating of the wire. Thesesolenoids, moreover, are in general wound with several layers of wire,the layers also being separated from each other only by the insulatingcoatings of the wires. Such' solenoids are well adapted to be used inconjunction with condensers having solid dielectries for the purpose oftuning circuits to low frequencies; but neither such coils nor suchcondensers are available for the purpose of tuning circuits to such highfrequencies as are concerned in the present invention. In

sorbed in the solid dielectric of the condenser due to dielectrichysteresis is excessive and the displacement-currents between theadjawell-defined selectivity for that frequency to the exclusion ofother frequencies,even to the exclusion'of frequencies difiering butslightly from the predetermined frequency, it is necits the case of highfrequencies the energy abt high frequencies as if they had a fixed re-.

sistance and inductance and no capacity, but partake more of thecharacter of conductors having distributed resistance, inductance,and-capacity. In fact, they may insome in-' stances behave with highfrequencies more like condensers than like conductors having fixedresistance and inductance and no capacity. Since ajcoil constructedinthe usual way behaves for high frequencies as a coninertia andelasticity ductor having distributed resistance, inductance, andcapacity, it follows that such a coil will show for high frequencies thesame quasi-resonance as is observed with low frequencies in long aeriallines and cables-4'. e., that it will per se and without theintermediary of a condenser show a slight degree of selectivity for someparticular frequencyand for certain multiples of that frequency just asa stretched string which has distributed will respond to a particulartone called its fundamental and to all other tones whose periods arealiquot parts of the periods of that fundamental;

but it is not with such quasi-resonance that the present invention iscarried into effect, and I wish it understood that I here disclaim anysystem employing distributed inductance and capacity as a means oftuning the reso-' nant circuits described in this specification.

,A general criterion which determines the utilityof a coil for tuning acircuit to a particular high frequency is thatthe potential energy ofthe displacement-currents in the coilshall be small compared to thekinetic V 1. energy of the conduction-current flowing through the coilwhen the coil is traversed by a current of that frequency.

I have found that for asingle-layercoil the following procedure issufficient for practical purposes. Determine the inductance of the coilby 5.

If the coil does not meet This willenablethe kin formulae to be found inthe text-books and treatises on electricity and magnetism.

coil to be determined for any particular. ourjrent and will also permitof the determination of what would be the potential gradient along ,thecoil for the current tof the fre-i quencyto be employed if the coil weredevoid of distributed electrostatic capacity. Next calculate theelectrostatic capacity between an end turn and each of the remainingturnsof the coil. These capacities, together with the potentialgradientfound,will enable the potential energy to be determined, and if theratio of the potential energy to the kinetic energy sofound benegligible compared to unity the coil will practically satisfy therequirements hereinbefore mentioned. the requirements,

etic energy of the Regarding the effect of a dielectric core in a coilto be used for tuninga circuit to a high frequency, it is sufiicienttostate that the preferred form of support for sucha coil is any skeletonframe which will hold the turns of wire in place without exposing muchsurface of contact to the wires and affording a minimum of opportunityfor the development of displacement-currents within itself.

In this specification I have spoken of elevated conductors,vertically-elevated conductors, and vertical conductors. I wish to beunderstood as including inthe term elevated conductors disposed at anangle to the earths surface ,as distinguished from horizontal.conductors disposed parallel to the earths surface. By the termsvertically elevated and vertical I refer to conductors whose dispositionwith regard to the earths surface is mainly or wholly ata right angle orvertical thereto, which is the particular form of elevated conductorpreferred by me for use in connection with my present improvement.

In this specification I have deseribed the development of free orunguided electromag netic signal-waves of a given frequency by employingin association with an elevated conductora circuit such as to producetherein forced simple harmonic electric vibrations of the frequencydesired. I have also described a method of receiving .or absorbing theenergy of free or unguided simple harmonic electromagnetic waves of onefrequency to the exclusion of waves of a different frequency byassociating with an elevated conductor a circuit made resonant to thefrequency of the waves whose energy is to be absorbed. The circuitwhereby forced simple harmonic electric vibrations are produced in theelevated conductor I have shown as a circuit containing a condenser anda self-induction coil so proportioned as to make the natural vibrationsof a frequency which is the frequency of the vibrations to be forced orimpressedin an elevated conductor. The circuit whereby the energy of theelectromagnetic waves of one frequency is absorbed to the exclusion ofthat of waves of another frequency is in like manner a circuitcontaining a condenser and a self-induction coil so proportioned as tomake the circuit resonant to a frequency which is the frequency of thewaves the energy of which is to be received. Bothof the circuits I havespoken of are tuned circuits, and they may be conveniently distinguishedwith reference to their respective functions by denominating the circuitemployed in the development of the vibrations as an oscillating. orsnorous-circuit and by denominating the circuit employed in thereception or absorption of the vibrations as a resonant circuit. 1preferto make this discrimination in nomenclature for the reason thatwhile both the circuits are resonant circuits, yet functionally onlythat one employed for receiving or absorbing is accurately so described.Except for this distinction in function it is well to,

note that all oscillating or sonorous circuits are resonant circuits,but only such resonant circuits as have their resistance less than thesquare root of the ratio of four times their inductance by theircapacity are oscillating or sonorous circuits. t I

Also throughout this specification I have describedthe electricaloscillations or vibrations and the free or unguided electromagneticwaves or radiations as simple harmonic.

It is the object of my present invention to approach as nearly aspossible to the perfect tion.

simple harmonicwave',and such object is attained to within such a degreeof precision as to preclude any possible interference with the operationof the system by any departure that can exist in the wave from theabsolute simple harmonic form. My reason for conevery precaution toobtain a true or absolute simple harmonic wave form.

Specifically,.though it may be possible to employ for the purpose ofmultiple and selective wireless telegraphy electric vibrations andradiations departing considerably from the simple harmonic type byemploying at the receiving end circuits selective to the fundamental ofsuch vibrations and radiations, yet it will only be through theselective reception of that simple harmonic component 0f the vibrationsor radiations which is their inndamental that the system will beoperat1ve.. The other simple harmonic components of the vibrations orradiations add nothing to the operation of the system. Moreover, if suchovertones exist in the waves emanating from a transmitting-station theirpresence will preclude the possibility of placing receiving-stations inthe immediate neighborhood of such transmitting-station for thereception of signal-waves of frequencies cor- It is for this reason thatI have taken.

responding to the frequencies of such overtones.

Whereas in the present specification I have used the term elevatedconductor todescribe the source of radiation of electromagnetic wavesdeveloped by forced electric vibrations impressed thereon, yet I deem itproper to point out that this expression should not be confused with theterm conductor when used in connection with systems wherein that term isemployed to denote a wire or other metallically-continuous conductorextending from a transmitting to a receivingstation. It is of courseobvious that in the art to which the present specification relates sucha conductor is wholly absent. The vertical metallically'rcontin uoussource of radiant energy is a structure the location and func tion ofwhich are confined entirely to the transmitting, or'it may be thereceiving, end of a system in which the conductor which connects thetransmitting and receiving sta-' tions is the non-metallicnon-conducting-in fact, dielectric-medium,whichis commonly called theether and which is by many assumed to be essential to the theory of thepropagation of electrical and magnetic force, radiant light, and radiantheat.

Having described my invention, I claim- 1. Ina system for developingfree or unguided simple harmonic electromagnetic signal-waves ofa'definite frequency, an elevated conductor and means for developingtherein forced simple harmonic electric vibrations of correspondingfrequency.

2. In a system for receiving the energy of free or unguided simpleharmonic electromagnetic signal-wavesof a definite frequency, to theexclusion of the energy of signal-waves of other frequencies, anelevated conducto and a resonant circuit associated with said conductorand attuned to the frequency of the waves, the energy of which is to' bereceived.

3. In a system for independently developing free or unguided simpleharmonic electromagnetic signal-waves of dilferent frequencies, anelevated conductor and means for independently developing thereinforced, simple harmonic, electric vibrations of different andcorresponding frequencies.

4. In a system for selectively receiving the energy of free or unguided,simple harmonic, electromagnetic signal-waves of difierent frequencies,each to the'exclusion of the test, an elevated conductor, and resonantcircuits associated with said conductor and each atof said conductorsforced simple harmonic elect ic vibrations corresponding to a differouto e of the said frequencies.

i6. In a system for selectively receiving the energy of free or unguidedsimple harmonic, electromagnetic signal-waves of diEerent frequencies, aplurality of elevated conductors elevated conductor, and each attunedto' a different one of the said frequencies. 7. In a system forproducing free and unguided electromagnetic signal-waves of a definitefrequency, an elevated conductor, a source of electrical. energy and. agroup of resonant circuitsinterposed between said elerial-waves, acondenser,

vated conductor and said source of electrical energy, said circuitsbeing attuned to the frequency of the waves to be developed.

8. In a systemfor receiving the energy of free or unguided simpleharmonic, electromagnetic signal-waves of one frequency to the exclusionof the energy of those of other frequencies, an elevated conductor, anelectric translating device, and a group of resonant circuits interposedbetween said elevated condevice,

of the waves, the energy of which is to be received.

9. In a system for developing free or unguided simple harmonic,electromagnetic sigmeans for charging and discharging said condenserthrough a closed circuit having inductance adapted toproduce under suchconditions simple harmonic electric vibrations, and means forcommunicating the vibrations so produced to an open circuit or elevatedconductor.

10. In a system for developing free orunguided, simple'har'monic,electromagnetic signal-waves, a condenser, means for charging -anddischarging said condenser through a closed circuit having inductanceadapted to produce under such conditions simple harmonic electricvibrations, means for communicating said vibrations toa resonant cir-.cuit or group thereof attuned to the frequency of these vibrations andmeans of communicating the resulting electrical vibrations in saidresonant circuit or group thereof to an open circuit or elevatedconductor;

11. A circuit resonant to a given High frequency comprising a coilhaving the amplitude of its potential energy small compared to theamplitude of its kinetic energy when it issupporting a current of saidgiven high frequency,

and a'condenser adapted to balance by its reactance, the reactance ofsaid coil for said given high frequency.

12. In a circuit resonant to agiven high frequency, a coil having theamplitude of its potential energy small compared to the am- 5 plitude ofits kinetic energy when supporting a current of said given highfrequency.

13. In a system for selectively receiving the free or unguided,

energy of free or unguided simple harmonic,

electromagnetic,signal-waves of different frequencies, a plurality ofelevated conductors, each associated with a circuit resonant to theparticular frequency of the electromagnetic waves, the energy of whichit is to receive.

15. In a system for selectively receiving the energy of free or unguidedsimple harmonic, electromagnetic,signal-waves of difierent frequencies,a plurality of elevated conductors, each associated with a group ofcircuits resonant to the particular frequency of the electromagneticwaves the energy of which it is to receive. 1 r

16; In asystem for selectively receiving the energy of free or unguidedsimple harmonic, electromagneticsignal-waves of different frequencies,an elevated conductor and a plurality of groups of resonantcircuits'associated with said elevated conductor, each of said groups ofcircuits being resonant to the particular frequencies of theelectromagnetic waves, the energy of which it is to receive.

17. Ina system for receiving the energy of simple harmonic,electromagnetic signal-waves of a definite frequency to the exclusion ofenergy of signal-waves of other frequencies, an elevated conductor and agroup of resonant circuits associated with said conductor and attunedtothe frequency the energy of whichis to be reof the waves, ceived.

and a plu- 18. In a system for selectively receiving the energy of freeor unguided, simple harmonic, electromagnetic signal-waves of differentfrequencies, eachto the exclusion of the rest, an

elevated conductor and a plurality of resonant circuits associated withsaid conductor and each attuned to the frequency of adifferent' one ofthe trains of Waves, the energy of which is to be received.

I to

19 In a system for selectively receiving the I energy of free orunguided simple harmonic, electromagnetic signal-waves of difierentfrequencies, a plurality of elevated conductors corresponding in.n umberto the n umber of different frequencies to be received, and groups a ofresonant circuits each'associated with a different elevated conductor,and each attuned to a dilferent one of the said frequencies.

. 20 In a system for developing free or un guided simple harmonic,electromagnetic signal-waves or radiations, anelevated conductor,associated closed oscillating. circuits,

means for disturbing the eleetricalequillbrium of said oscillatingcircuits, and means for swamping the effect of the mutual inductancebetween said circuit and the elevated conductor.

7 22. In a system for receiving the energy of 7 simple harmonic,electromagnetic waves of a given frequency, to the exclusion of likewaves of different frequencies, an elevated conductor, a circuitassociated with said elevated conductor and made resonant to thefrequency of the electromagnetic-waves, the energy of which is to bereceived, by the condenser and an auxiliary inductance-coil whoseinductance is suflicient to swamp the effect of the mutual inductancebetween the associated circuit and the elevated cond ctor.

23. In asystem for recei yng the energy-of simple harmonic,electromagnetic waves of one frequency, to the exclusion of like wavesof difierent frequencies, an elevated conductor, associated circuitseach resonant to the frequency of the electromagnetic waves to bereceived, and each having sufficient auxilia'ry inductance to swamp theefiect of the mutual inductance between it and the other associatedcircuits and between it and the elevated conductor.

24. In a system for developing simple harmonic, electromagneticsignal-waves or radiations of a given frequency,- ametallicallycontinuous-vertical oscillator and means for impressingthereon simple harmonic, electrical, oscillations of the same frequency.I 25. In a system for simultaneously developing simple harmonic,electromagnetic, signal-waves of dilferent frequencies, a metallicallycontinuous vertical, oscillator, and means for impressing thereon simpleharmonic, electrical oscillations of the same frequencies.

26. In a system for receiving the energy of free or unguided, simpleharmonic, electromagnetic waves, an elevated conductor, a circuitassociated with said elevated conductor and resonant to the frequency ofthe electromagnetic waves, and'an electric translating device shuntedaround free or unguided,

the terminals of one of the elements of said resonant circuit.

27. In a system for receiving the energy of simple harmonic,electromagnetic waves, an elevated conductor, a group of resonantcircuits associated with said resonant conductor, resonant to the fre-.quency of the electromagnetic waves, and an electric: translating deviceshunted around the terminals of that one-of said resonant cir-,

cuits which is farthest removedfrom the ele- -vated conductor.

28. In a system for receiving the energy of free or unguided, simpleharmonic, electromagnetic waves, an elevated conductor and an electrictranslating device forming one of the elements of a resonant circuitassociated with said. elevated conductor and resonant to the frequencyof the electromagnetic waves.

29. In a system for receiving the energy of simple harmonic,electromagnetic waves of a given frequency, to the exclusion of likewaves of different frequencies, an elevated conductor, a circuitassociated with said elevated conductor and made resonant to thefrequency of the electromagnetic waves, the energy of which is to bereceived, and means for swamping the effect of the mutual inductancebetween said circuit and the elevated conductor.

30. In a system for receiving the energy of simple harmonic, onefrequency, to the exclusion of like waves of difierent' frequencies, anelevated conductor, associated circuits each resonant to the frequencyof the electromagnetic waves to be received, and means in each of saidcircuits for swamping the effect of the mutual inductance between it andthe other circuits and between it and the elevated conductor.

31. In a system for receiving the energy of free or unguided, simpleharmonic, electromagnetic signal-waves of a definite frequency, to theexclusion of the energy of signal-waves of other frequencies, anelevated conductor, a resonant circuit associated with said con ducttirand attuned to the frequency of the waves, the energy of which is to bereceived and means'for swamping the elfect of the mutual inductancebetween said circuit and the elevated conductor.

32. In a system for selectively receiving the energy of free orunguided, simple harmonic,

electromagnetic signal-waves of dilferent frequencies, each to theexclusion of the rest, an

elevated conductor, resonant circuits associated with said conductor andeach attuned to the frequency of a different one of the trains of waves,the energy of which is to be received,

and means for swamping the effect of the mutual inductance between saidcircuit and the elevated conductor.

33'. Ina system for selectively receiving theenergy of free or unguided,simple harmonic,

electromagnetic, signal-waves of different frequencies, a plsrality ofelevated conductors corresponding in number to the number of difierentfrequencies to be received, resonant circuits each associated with adifferent ele-- vated conductor and each attuned to a different one ofthe said frequencies, and meansina each of said circuits for swampingthe eifect' of the mutual inductance between'it and the other circuitsand between it and the elevated conductor. t

34. Ina system for'producing free and unguided, electromagneticsignalwaves of a definite frequency, an elevated conductor, a

source of electrical energy,

a group of resonant circuits interposedbetween said elevated conductorand said source of electrical energy,

said circuits being attuned to the frequency of the wavesto bedeveloped, and means in each of said circuits for swampingthe effect ofthe mutual inductance between it and the other circuits and between itand the elevated conductor. U

In a system for receiving the energy of free or unguided, simpleharmonic, electrounagnetic signal-waves of one frequency, to

the exclusionof the energy of those of other frequencies, an elevatedconductor, an electrio translating device, a group of resonant circuitsinterposed between said elevated conductor and said electric translatingdevice, said circuits being resonant to the frequency of the waves, theenergy of which is to be received, and means in each of said circuitsfor swamping the elfectof the mutual inductance between it and theother'circuits and between a it and the elevated conductor.

36. In a system for developing free or unguided, simple harmonic,electromagnetic signal-waves, a condenser, means for chargmg anddischarging said condenser through a closed circuit having inductanceadaptedto produce under such conditions simple harmonic, electricvibrations, means for communicating the vibrations so produced to anelevated conductor, and means for swamping the efiect of the mutualindnctancebetween said circuit and the elevated conductor.

37. In a system for developing free or unguided, simple harmonic,electromagnetic signal-waves, a condenser, means for chargring anddischarging said condenser through a closed circuit havinginductanceadapted'to produce under such conditions simple harmonic,electric vibrations, means forcommunicating said vibrations to aresonant circuit or group thereof attuned to the frequency ofthesevibrations, means of communicating the resultingelectricalvibrations in said resonant circuit or group thereof to an elevatedconductor, and means in each of said circuits for swamping the effect ofthe mutual inductance between it and the other circuits and between itand the elevated conductor.

' 38 In a system for selectively receiving the energy of free orunguided, simple harmonic, electromagneticsignal-waves of differentfrequencies, an elevated conductor, a plurality of resonant circuitsassociated with said elevated conductor, each resonant to ,theparticular frequency, of the electromagnetic waves, the energy of whichit'is to receive, and means in each of said circuits for swam ping theeffect of the mutual inductance between it and the other circuits andbetween it and the elevated conductor.

" 39,. In a system for selectively receiving the energy, of free orunguided, simple harmonic, electromagnetic signal-waves of different hequencies, a plurality of elevated conductors, each associated with acircuit resonant to the particular frequency of the electromagneticwaves, the energy of which it is to receive, and means ineach of saidcircuits for swamping the eifectof the mutual inductance between it andthe other circuits and between it and the elevated conductor.' a

40. In a system for selectively receiving the energy of free orunguided, simple harmonic, electromagnetic signal-waves of differentfrequencies, a plurality of elevated conductors, each associated with agroup of circuits resonant'to the particular frequency of theelectromagnetic waves the energy of which it is to receive, and means ineach of said circuits for swamping the effect of the mutual inductancebetween it and the other circuits and between it and the elevatedconductor.

41. In a system for selectively receiving the .energy of free orunguided, simple harmonic,

electromagnetic signal-waves of different frequencies, an elevatedconductor, a plurality of groups of resonant circuits associated withsaid elevated conductor, each of said groups of circuits being resonantto the particular frequencies of,the electromagnetic waves, the energyof which it is to receive, and meansin each of said circuits forswamping the effect of the mutnal'inductance between it and the othercircuits and between it and the elevated conductor.

42. In a system for receiving the energy of free or unguided,simpleharmonic, electromagnetic signal waves of a definite frequency, tothe exclusion of energyof signalwaves of other frequencies,an elevatedcon ductor, a group of resonant circuits associated with said conductorattuned to the frequency of the waves, the energy of which is to bereceived, and means in each of said cir cuits for swamping the eifectofthe mutual inductance between it and the other circuits and between itand vthe elevated conductor.

43. In a system forselectively receiving the energy of free or unguided,simple harmonic, electromagnetic signal-waves of diiferent frequencies,each to the exclusion of the rest, an elevated conductor, a plurality ofresonant circuits associated with said conductors and each attuned tothe frequency of a diiferent one of the trains of waves, the energy ofwhich is to bereceived, and means in each of said circuits for swampingthe eifect of the mutual inductance between it and theother circuits andbetween it and the elevated conductor.

44. In a system for selectively receiving the energy of free orunguided, simple harmonic,

electromagnetic signal-waves of diiferent frequencies, a plurality ofelevated conductors corresponding in number to the number of differentfrequencies to be received, groups of resonant circuits each associatedwith a different elevated conductor, and each attuned to a diiferent oneof the said frequencies, and

means in each of said circuits for swamping the eifect of the mutualinductance between it and the other circuits and between it and theelevated conductor.

JOHN STONE STONE. In presence of- ALEX. P. BROWNE, ELLEN B. TOMLINSON.

